1. Field of the Invention
The present invention relates to a storage area network (SAN), and more particularly, to an access system in which each of a plurality of computer systems can make fast data accesses to a single file system created in one or more shared disk devices on the SAN.
2. Description of the Related Art
In recent years, storage area networks (SANS) have been implemented for providing fast networks which connect external storage devices with one another, and between storage devices and computers. The SAN is particularly effective when a plurality of servers are associated to provide a certain functionality, and when a single shared disk device having a large capacity is shared by a plurality of servers. The introduction of SAN having such a topology can result in improved processing performance of servers, and a reduced load on a network between computers, such as LAN (Local Area Network), WAN (Wide Area Network), and the like for intermediating communications between servers and clients.
Conventionally, in a system which comprises a client, a server, a SAN, and a shared disk device provided on the SAN, a functionality of the client device for accessing the shared disk device, i.e., a client functionality is installed in a kernel of an operating system (OS) in the client device.
Japanese patent laid-open application No. 11-120063 (JP-11-120063-A), for example, discloses a system in which a disk device is shared among a plurality of computers through a network. This system is intended to reduce a load on a server which is responsible for file management, and to avoid transferring file data through a network to provide faster processing. In this system, the server is responsive to a request from a client on the network to send management information on a requested file to the requesting client, such that the requesting client directly accesses the shared disk through the SAN based on the management information sent thereto.
However, the conventional accessing method to the shared disk on the SAN as described above implies the following problems.
First, since a SAN accessing functionality is installed in the kernel of each client, this functionality depends on the version of the kernel. Therefore, a functionality for accessing the storage area network must be re-installed for each version of the kernel.
Second, since a variety of methods exist for implementing accesses to the SAN depending on the platforms or operating systems, the kernel in the client must be adapted by re-compiling, relinking, and the like for installing the functionality of a client in a different platform. Consequently, the porting of the client functionality entails significant efforts and cost.
Third, when the SAN access functionality is included in kernel facilities, bugs included in the access functionality, if any, could affect the overall system of the SAN.